Breath

Chemistry of Breath

We exhale mostly the same stuff that what we inhale. There is only about 10% difference in chemical composition of exhaled and inhaled air. This difference accounts for the state of our health and metabolism.

The air we inhale is roughly 78% nitrogen, 21% oxygen, 0.96% argon and 0.04% carbon dioxide, helium, water, and other gases, by volume. The quality of air varies.
EPA monitors five major air pollutants regulated by the Clean Air Act:
ground-level ozone, particle pollution (also known as particulate
matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. Underwater divers often breathe slightly different oxygen-rich or helium-rich gas mixes.

Normal human breath contains a great number of alkanes and monomethylated alkanes.
Food
and beverages can influence what chemicals we breath out. For example,
allyl thiosulfinates (mainly allicin) are detected in breath of those who ate
garlic.
Chemicals in breath also depend on the age, exercise, and health/disease status.
Most
of the compounds that cause bad breath (hydrogen sulfide, methyl
mercaptan, cadaverine, putrescine, skatole) are the waste products of
anaerobic bacteria (more specifically Gram-negative anaerobic
bacteria).

Here are a few examples of breath chemistry studies:
- Dimethyl
sulfide (and other sulfur compounds), acetone (ketone), 2-butanone and 2-pentanone (methyl ketones) are increased in breath of
liver patients, while indole and dimethyl selenide are decreased. People perceive the odor as mousy, sweet fecal and fishy.
-
Sulfur-containing compounds such as methanethiol and hydrogen sulfide are present at significantly higher concentrations in the breath of lung cancer patients and flatus of colon cancer patients. These compounds are produced when glucose reacts with methionine or its metabolites homocysteine or cysteine.
- Camphor, Bicyclo[2.2.1]heptan-2-one,1,7,7-trimethyl-,(IS)-, 2-Cyclohexene-1-methanol,alph,alpha4-trimetyl-, p-menth-1-en-8-ol are among major VOC identifiers of primary lung cancer in breath.
- Oxidative stress that accompanies transplant
rejection degrades polyunsaturated fatty acids in membranes by lipid
peroxidation, which releases alkanes and methylalkanes excreted in the
breath.
- Components of petrole and their methyl-derivatives such as 4-methyloctane, methylpentadecane, methylxecadecane, butane, xecane, and pentane are indicative of heart disease. Some of these compounds are used by insects in chemical communication. Odors range from floral to cement and racing motorcycles
- Alkanes ethane and pentane, constituents of fuels, are indicative of Asthma, COPD and Cystic Fibrosis
- Breath pentane (an alkane with the formula C5H12, generated by peroxidation of cellular fatty acids) is a
determinant of inflammation and has been correlated with inflammatory bowel disease
- Derivatives of cyclic hydrocarbons - such as Cyclopropane, Limonene, Benzene, Longifolene, and simpler hydrocarbons - Tridecane, Tetradecane, Pentadecane, along with fatty alcohols (octanol) were found in breath of breast cancer patients. Smell of these compounds ranges from lemony to gasoline fumes, rubber and stinky bugs
- Naphthalene, 1-methyl-, 3-heptanone,
methylcyclododecane, heptane, 2,2,4,6,6-pentamethyl-, benzene,
1-methyl-4-(1-methylethyl)-, and cyclohexane, 1,4-dimethyl-,
monomethylated alkanes (dimethylcyclohexane, methylheptane, methylcyclododecane, tetramethylbenzene)
are the
most abundant in active pulmonary tuberculosis.
- Volatile sulfur
compounds such as hydrogen sulfide, methyl mercaptan, and dimethyl
sulfide primarily produced by anaerobic bacteria are considered to be
the major gases associated with breath malodor. Other malodor chemicals include ammonia, aliphatic amines, branched chain fatty acids, indoles, and phenols.
- The concentrations of several of the C4 to C20 alkanes and methylated alkanes increases with age. Unsaturated aldehyde 2-Nonenal is also associated with aging. The odor is perceived as somewhat fatty and earthy with notes of roots of the iris plants, cucumber, buckwheat and aged beer.
- A fruity odor to the breath is due to excess acetone. This is a sign of ketoacidosis,
which may occur in diabetes. Acetone is a byproduct of fat catabolism related to
circadian rhythmisity and its concentration increase overnight, reaching maximum levels 2-3
hours before lights on.
- Breath that smells like feces can occur with prolonged vomiting,
especially when there is a bowel
obstruction.
- Ammonia-like odor (also described as
urine-like or "fishy") is present in people with chronic
kidney failure , uremia and other stages of renal disease. It occurs due to nitrogen-containing compiunds, namely amines dimethylamine (DMA) and trimethylamine(TMA).
- Breath isoprene concentrations depend on short-term physical activity and increase overnight.
- Isoprene is also associated with problems in cholesterol metabolism. It smells like new rubber tubing or oak forest and repels insects.
- Bacteria-specific volatiles in the
breath can tell about sinus infection, although signatures of different bacteria
greatly differ.